In general, the film scanning device has a planar light source disposed on one side of a film. During the process of scanning a film (such as a negative or a transparent document), light emitted by the planar light source disposed on one side of the film passes through the film and is received by the scanning device, to obtain an image information of the film. Before scanning, the film scanning device needs to be corrected for eliminating errors in image information caused by non-uniform, planar light source.
According to the generally known correction method, the planar light source is divided into a scan region for emitting light onto the film and a correction region for emitting light for correction. During correction, the optical image sensor of the scanning device is moved to the correction region, reads a backlight distribution information obtained from the correction region as a correction signal, and corrects the signal obtained during film scanning according to the correction signal. The above prior method is directed to correcting the planar light source which has a larger volume, but is not applicable to the portable scanner, particularly sheetfed scanning device which uses a compact and small-sized line light source as a light source during film scanning. When the above method is adapted in the portable scanner, the correction result is poor, and the scan effect is negatively affected.